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Fluctuations in soil greenhouse gas (GHG) are an important part of the terrestrial ecosystem carbon-nitrogen cycle, but uncertainties remain about the dynamic change and budget assessment of soil GHG flux. Using high frequency and consecutive soil GHG fluxes measured with an automatic dynamic chamber system, we tested the applicability of the current Forest-DNDC model in simulating soil CH4, CO2 and N2O fluxes in a temperate broad-leaved Korean pine forest at Changbai Mountain. The results showed that the Forest-DNDC model reproduced general patterns of environmental variables, however, simulated seasonal variation in soil temperature, snow melt processes and soil moisture partly deviated from measured variables, especially during the non-growing season. The modeled CH4 flux was close to the field measurement and co-varied mainly with soil temperature and snowpack. The modeled soil CO2 flux had the same seasonal trend to that of the observation along with variation in temperature, however, simulated CO2 flux in the growing season was underestimated. The modeled N2O flux attained a peak in summer due to the influence of temperature, which was apparently different from the observed peak of N2O flux in the freeze-thaw period. Meanwhile, both modeled CO2 flux and N2O flux were dampened by rainfall events. Apart from consistent estimation of annual soil CH4 flux, the annual accumulation of CO2 and N2O was underestimated. It is still necessary to further optimize model parameters and processes using long-term high-frequency observation data, especially transference of heat and water in soil and GHG producing mechanism. Continues work will improve modeling, ecosystem carbon-nitrogen budget assessment and estimation of soil GHGs flux from the site to the region.

Understanding the temperature sensitivity (Q(10)) of soil organic matter (SOM) decomposition is important for predicting soil carbon (C) sequestration in terrestrial ecosystems under warming scenarios. Whether Q(10) varies predictably with ecosystem succession and the ways in which the stoichiometry of input SOM influences Q(10) remain largely unknown. We investigate these issues using a grassland succession series from free-grazing to 31-year grazing-exclusion grasslands in Inner Mongolia, and an incubation experiment performed at six temperatures (0, 5, 10, 15, 20, and 25 degrees C) and with four substrates: control (CK), glucose (GLU), mixed grass leaf (GRA), and Medicago falcata leaf (MED). The results showed that basal soil respiration (20 degrees C) and microbial biomass C (MBC) logarithmically decreased with grassland succession. Q(10) decreased logarithmically from 1.43 in free-grazing grasslands to 1.22 in 31-year grazing-exclusion grasslands. Q(10) increased significantly with the addition of substrates, and the Q(10) levels increased with increase in N:C ratios of substrate. Moreover, accumulated C mineralization was controlled by the N:C ratio of newly input SOM and by incubation temperature. Changes in Q(10) with grassland ecosystem succession are controlled by the stoichiometry of newly input SOM, MBC, and SOM quality, and the combined effects of which could partially explain the mechanisms underlying soil C sequestration in the long-term grazing-exclusion grasslands in Inner Mongolia, China. The findings highlight the effect of substrate stoichiometry on Q(10) which requires further study.

The changes of soil C:N:P ratios and pH under nitrogen deposition,its effect on soil organic matter and litter decomposition and the possible soil microbial mechanism are the new position and scientific research front of terrestrial ecosystem and global change.The paper based on ecological stoichiometry and soil microbial ecology,summarized the basic theory,new advances,hot and difficult points of research on the effect of nitrogen deposition on soil organic matter and litter decomposition and the microbial mechanism,to advance the research of terrestrial underground ecology under global change.The continuing increasing nitrogen deposition accelerated the phosphorus cycling of forest ecosystem,caused phosphorus limitation.Nitrogen deposition not only changed soil organic matter and litter C:N:P ratios and decreased soil pH,but also changed soil microbial components of carbon,nitrogen and phosphorus,composition of bacterium,fungus and actinomycetes,the key enzymes for decomposition of carbon,nitrogen and phosphorus.The effects of nitrogen deposition on soil organic matter and litter decomposition have three states: motivation,suppression,no effect,the reasons for the different effect maybe come from different microbial effect.Leaves had obvious resorption of nitrogen and phosphorus,but root had less resorption rate,which caused clearly different C:N:P ratios between soil organic matter.The molecular methods based on DNA/RNA provided advanced tools for soil microbial ecology research,which would promote researches on microbial mechanism of soil organic matter and litter decomposition.